DESCRIPTION (Adapted from abstract): The project is aimed at understanding how to enhance two-photon absorption cross-sections of organic molecules to develop two-photon fluorophores. This could greatly enhance the applicability of two-photon fluorescence scanning microscopy (TPFSM). Guidelines for the synthesis of suitable molecules include high two-photon absorption cross section, high fluorescence quantum yield, tunable hydrophilicity, incorporation of functional groups for selective labeling, and photochemical stability to prevent rapid bleaching under laser irradiation.